Means for measuring electrical energy.



J. C. WILSON MEANS FOR MEASURiNG ELECTRICAL ENERGY.

APPLICATION FILED AUG. 14. 1913.

1,236, l 30.. Patented Aug. 7, 1917.

2 SHEETS-SHEET I.

I. C. WILSON.

MEANS FOR MEASURING ELECTRICAL ENERGY.

APPLICATION FILED AUG. I4. I9I3.

' 1,36,130v Patented Aug. 7, 1917.

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JOHN C. WILSON, OF MILWAUKEE, WISCONSIN, ASSIGNOR TO THE CUTLER-HAMMERMFG. 00., 0F MILWAUKEE, WISCONSIN, A CORPORATION OF WISCONSIN.

MEANS FOR MEASURING ELECTRICAL ENERGY.

Specification of Letters Patent.

Patented Aug. '2', 191%.

Application filed August 14, 1913. Serial No. 784,684.

To all whom it may concern:

Be it known that I, JOHN 0. WILSON, a citizen of the United States,residing at Milwaukee, in the county of Milwaukee and,

State of Wisconsin, have invented new and useful Improvements in Meansfor Measuring Electrical Energy, of which the following is a full,clear, concise, and exact description, reference being had to theaccompanying drawing, forming a part of this specification.

My invention relates to means for measuring electric energy.

The object of my invention, generally speaking, is to provide improvedmeans which shall measure electric energy accurately under widelyvarying conditions.

The integrating wattmeters ordinarily used in commercial service areconnected across the mains with their field coils in series with theload and their armatures in parallel relation therewith. The torquetending to rotate the armature shaft is thus proportional to the productof the series coil amperes and the armature voltage. The retarding'action of the usual disk which rotates between magnets isproportional to the speed of rotation. Where it is desired to regulatethe load by means of a rheostat connected in series therewith, however,such wattmeters do not give reliable results for the reason that thereis a variation of current in the voltage coil of the meter resulting invariations in temperature, and, hence,

described in the Patent to Carl C. Thomas,

No. 1,222,492, of April 10th, 1917.

A further object is to provide compensating means for a wattmeter, whichshall be independent of and external to said meter, whereby changes inthe structure of the wattmeter proper are not required.

I have illustrated somewhat diagrammatically in the accompanyingdrawings several embodiments of the invention. The invention may beembodied in other forms, of course; and accordingly I do not'limitmyself to the present showing.

Figure 1 shows a Wattmeter connected with a suitable load, the latterhaving a regllilating rheostat connected in series therewit i Fig. 2shows a wattmeter connected with the same load and provided withcompensating means to render accurate the readings thereof undervariations in voltage due to the operation of the rheostat.

Fig. 3 is a somewhat similar view showing certain vmodifications in thecompensating means.

Fig. 4 shows a modified form of compensating means.

Figs. 5, 6 and 7 are explanatory diagrams.

Fig. 8 is a further modification of compensating means.

In the various figures, the positive and negative supply mains areindicated by reference letters 1, 2. A suitable load 3 is connectedacross said mains in series with a regulating rheostat 4, which may beof any approved type. The load 3 may be assumed to be the heating coilof a fluid meter such as described in the Thomas patent above referredto, although the showing is merely diagrammatic and therefore, said loadmay be assumed to be almost any means for consuming electric energy. In

'order to measure the energy consumed by said load, I have illustrated asuitable wattmeter 5. This instrument may be assumed to be a suitablewatthour meter provided with a train of gears and a dial on which thewatthours may be read directly. Said wattmeter is provided'with theusual parts, most of which are not illustrated as they form no part ofthe present invention. The rotating armature 6, however, is indicated onthe diagram, said armature being supported on a suitable spindle. Onthis same spindle is mounted the usual metallic disk, said disk rotatingbetween magnet poles to give the necessary braking effect. Around thearmature the usual series coils 7 are arranged, the latter beingconnected in series with the load 3.

The armature 6 is connected across .1131.

load 3 and usually has in circuit therewith a resistance 8, which cutsdown the voltage drop across said armature. WVith this arrangement,andassuming that the value of the regulating resistance 4 remainsconstant, the torque tending to rotate the armature is proportional tothe voltage across the same, multiplied by the current in the fieldcoils expressed in amperes. The retarding action of the magnets on thedisk is proportional to its speed of rotation. The friction of the.rotating element may be compensated for in various ways. The provision'of a compensating coil 9 connected across the armature and arrangedadjacent to the field coils so as to augment the latter, is one wellknown means for accomplishing this result. The frictional torque isnearly constant for different speeds and inasmuch as the current, bothin the armature and in the compensating coil 9, is practically constantat different loads, the wattmeter readings indicated on the dial will beaccurate, even where the load 8 is assumed to be an incandescentlighting circuit, for example, the resistance of which may be varied byturning off or on more lamps.

Where said load is an electric heating coil in such a fluid meter asthat referred to above, or where for other reasons it is desirable ornecessary to operate thecontrolling rheostat 4 to vary the resistance inseries with said load,\the meter will not read accurately. For example,as the resistance 4 is increased and the wattage in the heating unit 3decreases from full load to "a smaller value, the voltage across saidheating unit, as Well as the current through it, decreases. Thisdecreases the current through the voltage circuit of the wattmeter andas a result, there is a variation in the temperature of the differentelements, constituting the circuit, accompanied by a consequentvariation in their resistance, the latter being followed'by' a variationin the current flow therethough. Variations in the temperature of theatmosphere surrounding the meter also cause variations in the resistanceof the said circuit so that at high atmospheric temperature the currentflowing therethrough for a given voltage is less than at lowtemperature.

Furthermore, the braking disk varies in effectlveness for any givenspeed with var1atlons in temperature of said dlsk. This 1s due to theincreased resistance of said disk which cuts down the currents inducedtherein by the magnets. Accordingly, the retarding action of the diskdecreases as the temperature increases. Said. disk may not be affectedby the heat dissipated from the meter coils, as it is usually located atthe bottom of the meter housing, but it is affected, however, byvariations in atmospheric temperature.

It has been proposed heretofore to eliminate certain of the above errorsby making the conductors of the armature circuit and the braking disk ofsuch material that the increased resistance of the former and thedecreased retarding action of the latter will off-set each other. Thismeans that the armature circuit, including its resistance 8, must have atemperature coefficient equivalent to that of the disk. This dispositionof materials permits the instrument to be satisfactorily compensated forvariations in at mospheric temperatures. With such an arrangement,however, errors will be caused at the different loads by the variationin the voltage across the heating unit, the resultant variation incurrent through the armature circuit, and the consequent variation inthe resistance of said circuit, due to the heating effects of saidcurrent.

This error, due to variations in temperature of the armature circuitbecause of variations in current flowin through it, might be preventedby making the armature circuit of a material having a Zero temperaturec0- eflicient, but if this is 'done, variations in atmospherictemperature which affect the retarding action of the disk will no longerbe compensated.

Moreover, since the retarding or augmenting efl'ect (as the case may be)of the compensating current is about proportional to the product of thecurrent through the armature and the current through the compensatingcoil, this effect decreases very rapidiy as the load decreases, and atthe lower loads where the friction torque becomes an appreciablepercentage of the total torque, the compensating torque has decreased toa very low value, and at the low loads it becomes impossible to augmentthe armature torque sufiiciently by this means to compensatesatisfactorily for friction.

More specifically,it is an object of my invention to provide means forproperly compensating for the errors introduced into the readings due tothe conditions just described,

In order to understand more fully the nature of the above inaccuracies,encountered when attempt is made to' measure with an ordinary watthourmeter varying wattages due to varying voltages across a fixedresistance, reference may be had to Fig. 5, in which a curve 10 isplotted, the abscissa of which represents percentage of load up to 100%,and the ordinates of which represent percentage of error of thereadings, the base line representing zero error. The values indicated bythis curve are taken on the assumption that the instrument has been sodesigned that its accuracy is not effected by variations in atmospherictemperature. Said curve has two important characteristic features.Beginning at its highest point to the left of the middle, it graduallydrops 01f to full load due to the increased temperaraseaao ture of thevoltage circuit during increased loads. Said curve gradually falls offfrom the maximum point as zero load is 'approached because of theincreasing ratio of frictional torque to turning torque. It is apparentthat the above features cannot be compensated for by any of the usualmethods.

Before describing more fully my improved compensating means forovercoming the above diificulty, reference may be had to Fig. 6, inwhich is shown a curve 11 plotted with reference to curve 10 in Fig. 5and showing' the values of the voltage at each different load,-which, ifapplied across the compensating coil of the wattmeter, would increase orretard the movement of the rotating elements 'so as to effect accurateintegration. Values of voltage having such direction that they willretard the movement of the rotating element are plotted below the zeroline and those having such directionas to. increase said movement areplotted above the line.

In Fig. 2, I have illustrated a compensating system, wherebysubstantially the de-' m'red voltage values may be-obtained. In saidfigure, the same reference characters are used as in Fig. l wherecorresponding parts are indicated. In addition, I have provided aresistance in two sections 12, .13

connected across the terminals of the rheostat 4, the combined value ofsaid resistances being large compared with that of the rheostat. To a vsuitable point commonto said resistance sections, a conductor 14 leadsto the compensating coil 9, a resistance 15 being usually included inthe circuit with said compensating coil. A second conductor 16 leadsfrom said compensating coil to a suitable point in the rheostatresistance 4. As the rheostat arm (indicated by the arrow) moves" fromthe left hand position toward the right, it is apparent that the voltageacross the compensating coil increases in "value until the full lineposition is reached. This is due to the fact that thevoltage across thecompensating coil is somewhat proportional to the voltage drop-acrossthat part of the rheostat between the position of the movable leverindicated by the full lines and its starting point. The voltage dropacross this section of the rheostat becomes a maximum when the rheostatlever reaches the full lineposition. After this position is passed, thevoltage drop across the above mentioned section of. the

rheostat must decrease on account of the gradual decreasing currentthrough the rheostat lever reaches such a position that the ratio of theresistance of that part of the rheostat between the full'line positionof the lever and the starting point to the resistance between the fullline position and the right hand position equals the ratio of resistance12 and 13, the voltage across the compensating coil will be zero. Aftersuch a point is reached the voltage across the compensating coil willincrease and will be in the opposite direction. I

The voltage values produced by the movement of the rheostat arm justdescribed are plotted in Fig. Gand indicated by the curve 17. Bycomparing this curve with the desired curve 11, it will be seen that thevalues actually attained are quite similar to the theoretically perfectvalues. In other words, the compensating system illustrated in Fig. 2gives very accurate results which answer every practical purpose.

By reference to the curves in Fig. 6, it will'be seen that the voltageacross the compensating coil at what has been called the full lineposition in Fig. 2-, is somewhat greater than is necessary. However, the

voltage can 'be further decreased or increased at this point byincreasing or decreasing the resistance 15 so that this value may besuitably modified. Furthermore, the point of attachment of the conductor16 to the resistance 4 may be moved either to the right or to the left,thereby shifting the position of the maximum voltage value in Fig. '6.Furthermore, the zero voltage value or the point where thecurves crossthe line in Fig. 6 may also be shifted from the right Or to the left byvarying the relative values of the resistances 12 and 13 which variesthe point indicated bythe right hand dotted line position of the arrowin Fig. 2. In other words, the above described method of compensation isvery'flexible and easily adjusted to suit the characteristic error foundin any type of watthour meter.

As a further refinement I have shown in Fig. 3 a diagram similar to thatshown in Fig. 2 except that instead of the single re sistance 15, Iprovide a plurality of resist ance branches 18, 19 in parallel. This arrangement has the eflect' of reducing the amount by which the actualvoltage values differ from the theoretically perfect voltage values. InFig. 7 I have plotted a curve 20 showing the percentage of error of thesystem illustrated in Fig. 2. By providing the further refinement inFig. 3, the percentage of error is further decreased. This increasedaccuracy is attained by increasing the number of nodes and thereforedecreasing the length pf each node. The number of parallel branchesand,'therefore, the number of nodes might be increased until the-curve20 conforms almost exactly with the line of zero error.

In Fig. 4 I have illustrated a modified form of compensating meanswherein the rheostat 21 operates a second rheostat 22, preferably bymeans of a mechanical conarms 24 and 25 both fast to a shaft 23, it is Ito be understood that this arrangement is merely intended as typical ofvarious mechanical connections which may be effected.

In Fig. 8 I have illustrated a modified form of compensating means whichpermits the compensating coil to be dispensed with. The rheostat 26,which is here illustrated as of the sliding type, although, of

course, it may be of any suitable type, is con nected directly in serieswith the armature 6 and is so designed as to vary the armature currentin the desired manner. Starting from full load the rheostat graduallyadds resistance to the armature circuituntil the point of maximum erroris reached. Then as the low load is approached the resistance isgradually cut out to allow more current to pass through the armature andthus compensate for the error as indicated by the left hand end of theerror curve in Fig. 5.

Among the many advantages of the above system of compensation over andabove the attainment of the requisite degree of accuracy, it maybementioned that the compensating system is external to and independent ofthe .meter, whereby the latter need not be of special construction, butmay simply be connected in. the desired circuit.

The invention, of course, is not limited to the detailed circuitconnections illustrated, nor is it dependent upon the use of anyparticular type of apparatus or device indicated diagrammatically on thedrawings. Accordingly, I desire to cover in the appended claims whateversuitable equivalent means may be employed to obtain the desired results.

WVhat I clai as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a load, a regulating rheostat in series therewith, anintegrating wattmeter connected to said load to indicate the wattageconsumption thereof, and means for compensating the wattmeter forvariations in the voltage across the load due to operation of saidrheostat.

2. In combination, a load, a regulating rheostat in series therewith, anintegrating wattmeter connected to said load to indi-v cate the wattageconsumption thereof, and means for-compensating the wattmeter forvariations in the voltage circuit tli'ereof due to changes in thepotential drop across said load.

3. In combination, a load subjected to a variable voltage, a wattmeterconnected thereto to indicate the electrical consumption thereof, andmeansexternal to and independent of said meter for modifying theoperation thereof to compensate for said variations in voltage.

4. In combination, a load, a regulating rheostat in series therewith, awattmeter connected thereto to indicate the electrical consumptionthereof 'and compensating means for said meter, said compensating meansbeing controlled by said regulating rheostat.

5. The combination with a heating unit and a variable resistance forcontrolling the energy consumed thereby, of ai wattmeter havin its fieldcoils in series with said unit, 1ts armature coils connected across saidunit, and acompensating field coil connected at one end to anintermediate point on said variable resistance and connected at theother end to points on opposite sides of said intermediate point.

6. The combination with a heating unit, of a variableresistanceconnected in series therewith, a wattmeter having its fieldcoils in series with said unit and its armature coils connected acrosssaid unit and a compensating field coil having connections from one endto an intermediate point on said variable resistance, a secondresistance of greater value than said first resistance connected inparallel with the latter and a connection from the other end of saidcompensating coil to an intermediate point on said second resistance.

7 A compensating circuit for a wattmeter which is connected in a circuithaving a variable resistance therein for varying the voltage applied tothe load whose "-watgage consumption the wattmeter is adapte toconnected to the ends of said resistance through a divided circuit eachbranch of which has a resistance therein.

- 8. In a compensating system for wattmeters a regulating resistance forvarying the voltage applied to .the load whose wattage consumption thewattmeter is adapted to measure, a second resistance in parallel to thefirst and connectionsfrom an intermediate point on each resistance to acompensating winding in the wattmeter.

9. In a compensating system, a wattmeter, a regulating resistance, asecond resistance connected in parallel therewith, a connection from anintermediate point on one of said resistances to said wattmeter and apluralityof parallel connections from successive points on said otherresistance to said wattmeter, said parallel connections includingadditional resistances.

10. In a compensating system for wattmeters, a compensating coil, avariable resistanQe, a connection from one terminal of said coil to anintermediate point on said resistance, a second resistance of highervalue than said first resistance connected at one end to an end of saidfirst resistance, and connected at the other end to the other end ofsaid first resistance and a connection from an intermediate point onsaid second resistance to the other end of said coil.

11. In combination, positive and negative supply mains, a heatingresistance and a,

regulating rheostat connected in series with each other across saidmains, a compensating coil for a wattmeter, a connection from anintermediate point on said rheostat' to said compensating meter coil, asecond resistance of higher value than said rheostat resistanceconnected to the terminals of the latter, a second connection from anintermediate point on said second resistance to. said compensating coiland a resistance included in said connections, whereby adjustment of therheostat from maximum load position to positions of decreasing load willcause first an increase in the volta c impressed on said compensatingcoil f0 lowed by a gradual decrease thereof.

12. The combination with a wattmeter of a compensating field coil andmeans for varying the voltage impressed on said compensating coil inaccordance with variations in the temperature and friction of the meterat the different loads being measured to compensate themeter fortemperature changes in the meter coils and for friction of the meterparts.

13. In a compensating system for wattmes ters, a compensating wattmetercoil, a variable resistance, a second resistance in paral- 'leltherewith, a conductor connected to an intermediate point on said secondresistance and adapted to be connected to one terminal of the wattmetercompensating coil, and a plurality of conductors extending in parallelfrom different points along said variable resistance to a common pointadapted to be connected to the other terminal of said compensating coil.

14. The method of measuring the electrical consumption ofa load inseries with a means for varying the energy supply thereto, whichconsists in using the current supply to said load and the voltage dropacross said load to operate a wattmeter and supplying the wattmeter withat supplemental voltage which is varied in accordance with variations inthe energy supply to compensate the wattmeter for variations in the.

load.

15. The method of 'compensatinga watts supplemental voltage to thewattmeter and varying said voltage in accordance with variations in thevariable resistance.

16. The method of compensating a wattmeter used to measure electricalenergy consumed by a resistance unit, the quantity of said energy beingvaried by varying the voltage supply to said unit, which consists invarying the torque in the wattmeter by means of a compensating coil andvarying the energy supply to said coil in accordance with. variations inthe voltage across said resistance.

17. The method of measuring the electrical energy consumption of a loadto which a variable voltage is supplied, which consists in using thecurrent supply to said load and the voltage drop across said load tooperate a wattmeter, and furnishing a separate supplemental supply ofenergy to the wattmeter which is varied in accordance with variations inthe temperature and friction of the meter at diflerent loads.

18. The combination with a source of energy of means for varying thesupply of energy from said source, an energy measuring means formeasuring the energy supply, means dependent upon the energy varyingmeans for compensating the energy measuring means for errors atdifferent rates of energy supply.

19. The combination with an wattmeter measuring a variable load of meansfor varying said load and means for compensating the errors in thewattmeter at different loads, said compensating means being dependent onthe load varying means.

20. The combination with an integrating wattmeter connected to anelectric circuit having a load connected thereto of means forcompensating the wattmeter for variations in the voltage across theload.

'21. The combination with an integrating wattmeter connected to anelectric circuit having a load connected thereto of means forautomatically compensating the wattmeter for variations in the voltageacross the load.

22. The combination with an integrating wattmeter connected to anelectric circuit having a load connected thereto of means comprisingparts independent of regular wattmeter operating means forcompensatcally compensating said wattmeter for variations in the voltageacross the load.

24. The combination with an electric circuit having a load connectedthereto of means for varying the voltage applied to electric said load,an integrating wattmeter for measurlng the Wattage consumption of saidload and means controlled by the voltage .varying means for compensatingthe Wattmeter for variations due to changes in the voltage across theload.

25, The combination with an' electric circuit having 'a load connectedthereto of means in series with said load for varying the voltageapplied thereto, an integrating Wattmeter for measuring the Wattageconsumption of said load and means controlled by the voltage varyingmeans for compensating the Wattmeter for variations in its operation due1 to changes in the voltage 7 across the load.

26. The combination with an electric circuit having a load connectedthereto of a rheostat in series with said load for varying the voltageapplied thereto, an integrating Wattmeter for measuring the Wattageconsumption of said load and means re sponsive to changes in therheostat for compensating the Wattmeter for variations in its operationdue to changes in the voltage across the load.

In witness whereof, I have hereunto subscribed my name in thepresence oftWo Witnesses,

JOHN 0. WILSON.

I Witnesses:

C. R. POE, F. H. HUBBARD.

